well I would say Earth
Our existing knowledge of astronomy is essential for these reasons (and many more):
Navigation.
Chronology.
Predicting tides.
Weather prediction.
Communication (think satellites).
Our current and future pursuit of astronomy is important for these reasons (and many more):
To better predict the weather.
To equip ourselves to deal with potentially disastrous collisions in the future.
To predict potential disruptions to communication, etc. caused by sunspot activity and solar flares.
To improve our scientific understanding of the nature of reality by observing the effects of extreme conditions (e.g. black holes).
To understand how to colonise other planets if we need to.
To understand better how life began on this planet, and the diversity of forms it may take in general.
hope this helps :)